In the production of automobiles, it is the usual practice as the assembled engine and transmission is moved along a sub-assembly line, to fill the transmission with transmission fluid as the assembled motor and transmission moves past a transmission filling position along the subassembly line. This is normally done with a transmission fluid pouring gun unit which is manually operated by an operator, and the amount of fluid which is poured into the transmission by the use of the gun is judged by the eye of the operator. Where there are a variety of transmissions, the level to which the transmission fluid should be poured into the transmission can vary, depending upon the type of transmission, and it is rather difficult for the operator to properly manually judge the proper level of the transmission fluid in the transmission.